Two-piece rotary metal-cutting tool and method for interconnecting the pieces

ABSTRACT

A tool includes a tool body and a cutting portion detachably mounted thereon, the tool being rotatable about a longitudinal center axis. The tool body includes flutes formed in an outer surface thereof, and a pair of forward projections at a front end thereof. The cutting portion includes front flutes formed in an external side thereof, and a pair of recesses extending circumferentially in communication with respective ones of the front flutes. To connect the cutting portion to the tool body, the cutting portion and tool body are converged longitudinally so that the projections enter the front flutes. Then, relative rotation is produced between the cutting portion and tool body to align the front flutes with the rear flutes while causing the projections to enter the recesses and form therewith a bayonet coupling.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a reissue of U.S. Pat. No. 5,971,673, which is acontinuation of application Ser. No. 08/929,462, filed Sep. 15, 1997,now U.S. Pat. No. 5,988,953 which claims the benefit of priority toSwedish Application No. 9603325 filed Sep. 13, 1996.

BACKGROUND OF THE INVENTION

The present invention relates to a tool for rotary, cutting machining,comprising a tool body and a cutting portion. The tool body has a frontsurface, and the cutting portion has a support surface provided toreleaseably abut against the front surface in a substantially radialplane. The tool body and the cutting portion comprises means whichcooperate for holding them together. The invention also relates to acutting portion and a tool body as well as a method for mounting acutting portion to a tool body.

PRIOR ART

It is previously known to use interchangeable cutting edges on differenttypes of tools for cutting machining, especially when cutting a metallicworkpiece. This technique however has practical limitations due tohandling reasons when it comes to milling and drilling tools whichrotate around a longitudinal axis.

Through DE-PS-367,010 and Burger U.S. Pat. No. 2,259,611, it ispreviously known to provide drills with lockable drill tips, wherein thedrill tip is retained with the aid of dove-tail profiles or with pressfit, respectively. The known tools however are impaired with drawbackssuch as bad torsion transferring ability and troublesome mounting anddismounting.

The present invention has as one object to provide drilling and millingtools with interchangeable cutting edges, which eliminates problemsassociated with known techniques.

Another object with the present invention is provide a rigid toolpreferably for drilling or milling wherein the cutting portioncooperates with the tool body via a bayonet coupling.

Another object of the present invention is to provide a rigid toolpreferably for drilling or milling wherein the cutting portion can beeasily exchanged by hand without time consuming screwing or soldering.

Another object of the present invention is to provide a tool with a selfcentering cutting portion.

SUMMARY OF THE INVENTION

These and other objects have been achieved by the present inventionwhich relates to a rotary metal-cutting tool comprising, in combination,a tool body and a cutting portion attached to the tool body. The toolbody includes a shank portion defining a longitudinal center axis, afront surface, and rear chip flutes formed in an external side surfaceof the shank portion for guiding chips rearwardly during a cuttingoperation. The cutting portion includes a rear support surface abuttingthe front surface, a front cutting face, and front chip flutes formed ina side surface of the cutting portion and intersecting the cutting faceto form cutting edges therewith. The tool body and cutting portion areinterconnected by a bayonet coupling formed by projections disposed onone of the tool body and cutting portion, and recesses formed in theother of the tool body and cutting portion. The projections arecircumferentially offset with respect to the flutes and extend generallylongitudinally. The recesses extend circumferentially from respectiveflutes. The flutes are sized to longitudinally receive respectiveprojections during longitudinal insertion or removal of the cuttingportion relative to the tool body. The cutting portion is rotatableabout the center axis relative to the tool body to transfer theprojections from the respective flutes and into the recesses whilebringing the front flutes into alignment with the rear flutes.

The invention also relates to a method of mounting a cutting portion toa tool body to form a metal-cutting rotary tool. The tool body includesa shank portion, a front surface, and rear chip flutes formed in anouter surface of the tool body. The cutting portion includes a supportsurface abutting the front surface, a cutting surface having cuttingedges, and front chip flutes formed in an outer surface of the cuttingportion. One of the tool body and cutting portion includes longitudinalprojections, and the other of the tool body and the cutting portionincludes circumferential recesses. Each recess communicates with arespective flute and extends less than 180°. The method comprises thesteps of:

-   A) converging the cutting portion and tool body longitudinally    toward one another to bring the projections into respective ones of    the flutes that communicate with the circumferential recesses; and-   B) effecting relative rotation between the tool body and cutting    portion to cause the projections to enter respective ones of the    recesses to bring the front flutes into alignment with the rear    flutes and to bring a stop surface of each projection into    longitudinally opposing relationship with a stop surface of a    respective recess for defining a bayonet connection preventing    longitudinal displacement of the cutting portion relative to the    tool body.

DESCRIPTION OF THE DRAWINGS

The objects and advantages of the invention will become apparent fromthe following detailed description of a preferred embodiment thereof inconnection with the accompanying drawing in which like numeralsdesignate like elements, and in which:

FIG. 1 shows a drilling tool according to the present invention, in anexploded perspective view;

FIG. 2 shows a cutting portion according to the present invention in abottom view;

FIG. 3 shows the cutting portion in a sectional view taken along theline III—III in FIG. 2;

FIG. 3A shows the cutting portion in a perspective view from below;

FIG. 4 shows the forward end surface of a tool body according to thepresent invention in top view;

FIG. 5 shows the drill shank in a sectional view taken along the lineV—V in FIG. 4;

FIGS. 6, 7 and 8 show cross-sections of a bayonet coupling of the tool;

FIG. 9 shows the assembled tool according to FIG. 1 in a magnified sideview.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

The embodiment of a tool 10 according to the invention shown in FIG. 1is a so called helix drill, which comprises a cutting portion or drilltip 11 and a drill body 12. The drill has a rotational direction R.

The drill tip 11 is provided with at least one cutting edge 19 in theforward end thereof facing away from the drill body 12, which tip isgiven different designs depending on the area of application.

The drill tip 11 is made of hard material, preferably cemented carbideand most preferably of injection molded cemented carbide, and comprisesa front cutting surface formed by two upper clearance faces 15, a lowersupport surface 16 as well as first and second curved surfaces 41, 18interconnecting the surfaces 15 and 16. All these surfaces andassociated edges are integrated as one piece with the drill tip andconsequently formed of the same material, i.e. preferably injectionmolded cemented carbide. The curved surfaces 18 form front chip flutesfor conducting cuttings rearwardly. Lines of intersection between thechip flutes 18 and the clearance faces 15 form main cutting edges 19,preferably via reinforcing chambers, not shown. Lines of intersectionbetween the first curved surfaces 41 and the chip flutes 18 formsecondary cutting edges 19′. The chip flute is shown as helical but mayalternatively be adapted for a drill body requiring straight chipflutes. The radially external parts between the chip flutes consist ofprotruding lands formed by the surfaces 41, each having acircumferential length G (FIG. 4). The largest diameter of the drill tipis the diametrical distance between the radially extreme points of thesecondary cutting edges. The height of the drill tip is substantiallythe same as the largest diameter of the tip, in order to minimize thewear from chips on the joint between the drill tip and the drill body.Flushing holes 23, extending substantially parallel with the rotationalaxis 22, extend through the drill tip from the support surface 16 to theorifice in respective upper clearance surface 15.

The support surface 16 according to FIGS. 2, 3 and 3A is substantiallyplanar but comprises a recess 50 at the transition between the supportsurface 16 and the land 41. Each recess 50 comprises a first free or endsurface 51 perpendicularly connected to both the land 41 and a secondfree surface 52 (see FIG. 8), which surface 52 in turn forms an acuteangle a with a first guiding surface 53 (see FIG. 6). The surface 53connects to a second guiding surface 54 oriented parallel to therotational axis 22, and which connects to the support surface 16 via aradius or an entering bevel 55. The surface 53 is inclined obliquelyrelative to the center axis 22 so as to face generally radially inwardlyand longitudinally rearwardly. As illustrated in FIG. 3, support surface16, recesses 50, and land 41 define a generally dovetail-shapedprojection. The recess 50 has a stop surface 56 (FIG. 3A) which isparallel to the axis 22 and which suitably lies in an axial plane whichintersects said axis. The recess 50 extends in a tangential directionfrom the chip flute 18 to about a midpoint of the circumferential lengthG of the associated land 41.

The drill body is made of a material which has a lower Young's modulusthan cemented carbide. The drill body has helical rear chip flutes 18A(or straight chip flutes if required) and these can extend along theentire outer surface of a shank portion 40 of the body or along only apart thereof. The drill body 12 is provided with a front surface 24 atthe end facing towards the drill tip 11, which surface 24 abuts againstthe support surface 16 of the drill tip 11. The largest diameter of thesupport surface 16 is larger than the largest diameter of the frontsurface 24 in order to minimize the wear from chips on the joint betweenthe drill tip and the drill body. The drill body also includes curvedsurfaces 41A forming lands. The front surface 24 is substantially planarbut comprises a projection 60 at the transition between the frontsurface 24 and the jacket surface of each land 41A. The height of theprojection is somewhat less than that of the depth of the recess 50.

Each projection 60 comprises a first free or end surface 61perpendicularly connected to the jacket surface 41A, said surface 61also perpendicularly connected to a second free surface 62, which in itsturn forms an acute angle π with a first guiding surface 63. The surface63 connects to a second guiding surface 64 oriented parallel to therotational axis 22. The surface 64 connects to the front surface 24 viaa radius 65. The surface 63 is oriented parallel to the surface 53 so asto face generally radially outwardly and longitudinally forwardly. Asillustrated in FIG. 5, the above-described surfaces, along with frontsurface 24, form a centrally disposed generally dovetail-shaped recess.The projection 60 has a stop surface 66, FIG. 9, which is parallel withthe axis 22 and which suitably lies in an axial plane which containssaid axis.

The smallest diameter of the front surface 24 is smaller than thelargest diameter of the drill tip but larger than the smallest diameterof the drill tip. The projection 60 extends in a tangential directionfrom the chip flute 18A to about the midpoint of the circumferentialtangential length G′ of the associated land 41A.

The stop surfaces 56 and 66, respectively, should be as far from therotational axis as possible for best moment transfer, i.e. they arearranged diametrically opposed each other. The drill tip must besymmetrically formed in order to retain the tool's concentrically atvarying strain, i.e. in order to keep the drill tip centered relative tothe drill body. The projections 60 and the recesses 50 lie at a distancefrom and substantially rearwardly of the associated cutting edge 19 inthe tool's rotational direction R.

Mounting of the drill tip 11 on the drill body 12 is done as follows.The drill tip 11 is brought in the axial direction towards the drillbody 12, so that each projection 60 is received in the associated chipflute 18 and so that the support surface 16 abuts against the frontsurface 24 thereby bringing the generally dove-tail shaped projection ofthe drill tip 11 into mating engagement with the generallydovetail-shaped recess of drill body 12. Then, the drill tip is rotatedin the direction R within an angle interval φ which is less than 360°,preferably less than 60°, relative to the drill body so that eachprojection 60 moves with a slide fit in the respective recess 50 untilthe stop surfaces 56 and 66 abut against each other. The drill tip 11 isnow anchored in the drill body 12 in a satisfactory manner. Thus, thepreformed spaces defined by the chip flutes 18 are used as the entranceand the exit of the bayonet coupling.

When the drill tip 11 must be replaced, the mounting procedure isreversed. The drill tip 11 then can be removed from the drill body 12and be exchanged, preferably with the aid of a suitable key inengagement with the chip flutes on the drill tip. The key is preferablyalso used during mounting of the drill tip.

The surfaces which during the drilling operation must be in engagementare surfaces 53 and 63 as well as the support surface 16 and the frontsurface 24. The surfaces 53 and 63 cooperate to hold the drill tip suchthat it cannot loosen in the feed direction, for example duringretraction of the tool. The surfaces 53 and 63 are preferably designedsuch that their cooperation results in some elastic deflection of theprojection 60 due to the slide fit. A limited contact surface betweensurfaces 54 and 64 can be allowed, but this implies an increased momentat the radius 65. The drill tip is self-centering in the tool body, i.e.it moves such that its axis coincides with the rotational axis 22 if ithas been displaced during the machining operation. The surface 55 willallow the radius 65 of the tool body to be relatively large. Thesurfaces 52 and 62 should not be in engagement with each other duringthe machining operation. That is realized by extending the surface 53(see FIG. 6). The clearance surfaces 51 and 61 should not be inengagement with each other during the machining operation, and thereforea gap P is always present between them (see FIG. 6). The gap P is in therange of 0.1-1.0 mm. The support surface 16 will be pressed by the feedforce against the front surface 24 during the machining operation, whichmeans that the elastic deflection of the projection 60 tends to decreasesomewhat, which however is counteracted because the projection 60 willbe bent radially inwardly due to pressure on the front surface 24 fromthe feed force.

The invention is useable also for milling cutters. The drill tip ispreferably coated with layers of, for example, Al₂O₃, TiN and/or TiCN.In certain cases, it can be well-founded to apply super hard materialsuch as CBN or PCD on the cutting edges. Alternatively ceramic materialcan be used at injection molding of the drill tips.

Although the present invention has been described in connection with apreferred embodiment thereof, it will be appreciated by those skilled inthe art that additions, modifications, substitutions and deletions notspecifically described may be made without departing from the spirit andscope of the invention as defined by the appended claims.

1. A rotary metal-cutting tool comprising, in combination, a tool bodyand a cutting portion attached to the tool body; the tool bodyincluding: a shank portion defining a longitudinal center axis, a frontsurface, and rear chip flutes formed in an external side surface of theshank for guiding chips rearwardly during a cutting operation; thecutting portion including: a rear support surface abutting the frontsurface, a front cutting surface, and front chip flutes formed in a sidesurface of the cutting portion and intersecting the cutting face to formcutting edges therewith; the tool body and cutting portion beinginterconnected by a dovetail-shaped bayonet coupling formed byprojections disposed on one of the tool body and cutting portion, andrecesses formed in the other of the tool body and cutting portion, theprojections being circumferentially offset with respect to the flutesand extending generally longitudinally; the recesses extendingcircumferentially from respective flutes; the flutes sized tolongitudinally receive respective projections during longitudinalinsertion or removal of the cutting portion relative to the tool body;the cutting portion being rotatable about the center axis relative tothe tool body to transfer the projections from the respective flutesinto the recesses while bringing the front and rear flutes into mutualalignment.
 2. The tool according to claim 1 wherein the recesses areformed in the cutting portion; and the projections are formed in thetool body.
 3. The tool according to claim 1 wherein the recesses areformed in the outer surface of the cutting portion; the cutting portionbeing rotatable relative to the tool body by an angle less than 360degrees.
 4. The tool according to claim 3 wherein the angle is less than60 degrees.
 5. The tool according to claim 1 wherein each of theprojections includes a first surface inclined obliquely relative to thecenter axis, the first surface facing generally radially inwardly andlongitudinally rearwardly; each of the recesses including a secondsurface inclined obliquely relative to the center axis, the secondsurface facing generally radially outwardly and longitudinally forwardlyand opposing a respective first surface to prevent relative longitudinalmovement of the cutting portion relative to the tool body.
 6. The toolaccording to claim 5 wherein a material from which the tool body isformed has a lower Young's modulus than a material from which thecutting portion is formed, to enable the projections to bend elasticallyin a radial direction during relative rotation between the cuttingportion and tool body.
 7. The tool according to claim 1 wherein each ofthe projections includes a first surface inclined obliquely relative tothe center axis, the first surface facing generally radially inwardlyand longitudinally rearwardly; each of the recesses including a secondsurface inclined obliquely relative to the center axis, the secondsurface facing generally radially outwardly and longitudinally forwardlyand opposing a respective first surface to prevent relative longitudinalmovement of the cutting portion relative to the tool body.
 8. The toolaccording to claim 6 wherein the outer surface of the cutting portiondefines a pair of lands extending circumferentially by equal distancesbetween the front flutes, each of the recesses extendingcircumferentially for a distance of about one-half of thecircumferential distance of a respective land, each of the projectionsextending circumferentially a distance substantially equal to that of arespective recess.
 9. The tool according to claim 1 wherein each of theprojections includes a first surface inclined obliquely relative to thecenter axis, the first surface facing generally radially inwardly andlongitudinally rearwardly; each of the recesses including a secondsurface inclined obliquely relative to the center axis, the secondsurface facing generally radially outwardly and longitudinally forwardlyand opposing a respective first surface to prevent relative longitudinalmovement of the cutting portion relative to the tool body.
 10. The toolaccording to claim 1 wherein each of the projections includes aforwardly facing end surface, and the recess includes a forwardly facingend surface, and the recess includes a rearwardly facing end surfacespaced from the forwardly facing end surface by a gap.
 11. A cementedcarbide cutting portion adapted to be connected to a tool body forrotary metal cutting, comprising a front cutting surface having at leastone cutting edge, a rear support surface, and at least one chip fluteformed in a side surface of the cutting portion for guiding cuttings,said cutting portion including coupling means defining a dovetail-shapedprojection and forming part of a bayonet coupling adapted to connect atool body with the cutting portion with a slide fit to an elasticallydeflecting portion of the tool body.
 12. The cutting portion accordingto claim 11 wherein the coupling means comprises a recess extendingcircumferentially less than 60 degrees.
 13. A rotary drill comprising: adrill body having a longitudinal axis and first and second opposed ends,one of said opposed ends comprising a centrally disposed dovetail-shapedrecess, and at least two circumferentially spaced projections, each ofsaid projections having a stop surface; a replaceable cemented carbidedrilling head having first and second opposed ends, one of said opposedends comprising a cutting portion, and the other of said opposed endscomprising a dovetail-shaped projection, said drilling head furthercomprising at least one stop surface; wherein the dovetail-shapedprojection mates with the dovetail-shaped recess with a slide fitelastically deflecting said projections and releasably connecting thedrilling head to the drill body.
 14. A method of attaching a drillinghead to a drill body, said drill body having a longitudinal axis andfirst and second opposed ends, one of said opposed ends comprising acentrally disposed dovetail-shaped recess, and at least twocircumferentially spaced projections, each of said projections having astop surface; said drilling head made of cemented carbide and havingfirst and second opposed ends, one of said opposed ends comprising acutting portion, and the other of said opposed ends comprising adovetail-shaped projection, said drilling head further comprising atleast one stop surface; wherein said method comprises: inserting saiddovetail-shaped projection into said dovetail-shaped recess; androtating said drilling head relative to said drill body such that aslide fit is formed between the drilling head and the drill body byelastic deflection of said projections, and the at least one stopsurface on said drilling head comes into engagement with at least one ofthe stop surfaces on one of the projections.
 15. A method for mounting acutting portion to a tool body to form a metal-cutting rotary tool; thetool body including a shank portion; a front surface, and rear chipflutes formed in an outer surface of the tool body; the cutting portionincluding a support surface abutting the front surface, a cuttingsurface having cutting edges, and front chip flutes formed in an outersurface of the cutting portion; one of the tool body and cutting portionincluding longitudinal projections, and the other of the tool body andcutting portion including circumferential recesses, each recesscommunicating with a respective flute and extending less than 180degrees; the method comprising the steps of: A) converging the cuttingportion and tool body longitudinally toward one another to bring theprojections into respective ones of the flutes that communicate with thecircumferential recesses; and B) effecting relative rotation between thetool body and cutting portion to cause the projections to enterrespective ones of the recesses to bring the front flutes into alignmentwith the rear flutes, and to bring a stop surface of each projectioninto longitudinally opposing relationship with a stop surface of arespective recess for defining a dovetail-shaped bayonet connectionpreventing longitudinal displacement of the cutting portion relative tothe tool body.
 16. A rotary metal-cutting tool comprising, incombination, a tool body and a cutting portion attached to the toolbody; the tool body comprising a shank portion defining a longitudinalcenter axis and rear chip flutes formed in an external side surface forguiding chips rearwardly during a cutting operation; the cutting portioncomprising a front cutting surface and front chip flutes formed in aside surface of the cutting portion and intersecting the cutting face toform cutting edges therewith; the tool body and cutting portion beinginterconnected by a dovetail-shaped bayonet coupling formed byprojections disposed on one of the tool body and cutting portion, andrecesses formed in the other of the tool body and cutting portion, theprojections being circumferentially offset with respect to the flutesand extending generally longitudinally, the recesses extendingcircumferentially from respective flutes, the flutes sized tolongitudinally receive respective projections during longitudinalinsertion or removal of the cutting portion relative to the tool body,the cutting portion being rotatable about the center axis relative tothe tool body to transfer the projections from the respective flutesinto the recesses with a slide fit, while bringing the front and rearflutes into mutual alignment.
 17. The tool according to claim 16,wherein the slide fit produces elastic deflection of the projections.18. A rotary metal-cutting tool comprising, in combination, a tool bodyand a cutting portion attached to the tool body; the tool bodycomprising a shank portion defining a longitudinal center axis and rearchip flutes formed in an external side surface for guiding chipsrearwardly during a cutting operation; the cutting portion comprising afront cutting surface and front chip flutes formed in a side surface ofthe cutting portion and intersecting the cutting face to form cuttingedges therewith; the tool body and cutting portion being interconnectedby a dovetail-shaped bayonet coupling formed by projections disposed onone of the tool body and cutting portion, and recesses formed in theother of the tool body and cutting portion, the projections beingcircumferentially offset with respect to the flutes, the recessesextending circumferentially from respective flutes, the flutes sized toreceive respective projections during insertion or removal of thecutting portion relative to the tool body, the bayonet coupling furthercomprising a first oblique surface and a second oblique surface, thecutting portion being rotatable about the center axis relative to thetool body to transfer the projections from the respective flutes intothe recesses with a slide fit between the first and second obliquesurfaces, while bringing the front and rear flutes into mutualalignment.
 19. The tool according to claim 18, wherein the slide fitproduces elastic deflection of the projections.